197 research outputs found
ASTE Simultaneous HCN(4-3) and HCO+(4-3) Observations of the Two Luminous Infrared Galaxies NGC 4418 and Arp 220
We report the results of HCN(J=4-3) and HCO+(J=4-3) observations of two
luminous infrared galaxies (LIRGs), NGC 4418 and Arp 220, made using the
Atacama Submillimeter Telescope Experiment (ASTE). The ASTE wide-band
correlator provided simultaneous observations of HCN(4-3) and HCO+(4-3) lines,
and a precise determination of their flux ratios. Both galaxies showed high
HCN(4-3) to HCO+(4-3) flux ratios of >2, possibly due to AGN-related phenomena.
The J = 4-3 to J = 1-0 transition flux ratios for HCN (HCO+) are similar to
those expected for fully thermalized (sub-thermally excited) gas in both
sources, in spite of HCN's higher critical density. If we assume collisional
excitation and neglect an infrared radiative pumping process, our non-LTE
analysis suggests that HCN traces gas with significantly higher density than
HCO+. In Arp 220, we separated the double-peaked HCN(4-3) emission into the
eastern and western nuclei, based on velocity information. We confirmed that
the eastern nucleus showed a higher HCN(4-3) to HCN(1-0) flux ratio, and thus
contained a larger amount of highly excited molecular gas than the western
nucleus.Comment: 21 pages, 4 figures, accepted for publication in PASJ (Vol.62, No.1,
2010 Feb 25 issue
Critical response of elastic-plastic SDOF systems with nonlinear viscous damping under simulated earthquake ground motions
Multi impulse with constant time interval is used as a representative of a long-duration earthquake ground motion. An analytical expression is derived for the elastic-plastic response of a single-degree-of-freedom (SDOF) model with nonlinear viscous damping subjected to the “critical multi impulse” which maximizes the response. The fact that only free vibration appears under such multi impulse enables the smart application of an energy approach in deriving the analytical expression for a complicated elastic-plastic response with nonlinear viscous damping. The nonlinear viscous damping characteristic for deformation is approximated in terms of a quadratic or elliptical function. The critical timing of the impulses is found to correspond to the zero restoring-force timing or the maximum velocity timing depending on the input level. It is shown that the nonlinearity in viscous damping causes a remarkable influence on the earthquake response in some cases. The reliability and accuracy of the proposed theory are investigated through the comparison with the results by the time-history response analysis to the tuned sine wave as a representative of the long-duration earthquake ground motion
Evolutionary phases of gas-rich galaxies in a galaxy cluster at z=1.46
We report a survey of molecular gas in galaxies in the XMMXCS J2215.9-1738
cluster at . We have detected emission lines from 17 galaxies within a
radius of from the cluster center, in Band 3 data of the Atacama
Large Millimeter/submillimeter Array (ALMA) with a coverage of 93 -- 95 GHz in
frequency and 2.33 arcmin in spatial direction. The lines are all
identified as CO =2--1 emission lines from cluster members at by
their redshifts and the colors of their optical and near-infrared (NIR)
counterparts. The line luminosities reach down to K km s pc. The spatial distribution of
galaxies with a detection of CO(2--1) suggests that they disappear from the
very center of the cluster. The phase-space diagram showing relative velocity
versus cluster-centric distance indicates that the gas-rich galaxies have
entered the cluster more recently than the gas-poor star-forming galaxies and
passive galaxies located in the virialized region of this cluster. The results
imply that the galaxies have experienced ram-pressure stripping and/or
strangulation during the course of infall towards the cluster center and then
the molecular gas in the galaxies at the cluster center is depleted by star
formation.Comment: 7 pages, 4 figures, 1 table, accepted for publication in the ApJ
Letter
A Search for Molecular Gas toward a BzK-selected Star-forming Galaxy at z = 2.044
We present a search for CO(3-2) emission in SDF-26821, a BzK-selected
star-forming galaxy (sBzK) at z = 2.044, using the 45-m telescope of the
Nobeyama Radio Observatory and the Nobeyama Millimeter Array. We do not detect
significant emission and derive 2 \sigma limits: the CO luminosity of L'CO <
3.1 x 10^10 K km s^{-1} pc^{-2}, the ratio of far-infrared luminosity to CO
luminosity of L_FIR/L'CO > 57 Lsun (K km s^{-1} pc^{-2})^{-1}, and the
molecular gas mass of M_H2 < 2.5 x 10^10 Msun, assuming a velocity width of 200
km s^{-1} and a CO-to-H2 conversion factor of alpha_CO=0.8 Msun (K km s^{-1}
pc^{-2})^{-1}. The ratio of L_FIR/L'CO, a measure of star formation efficiency
(SFE), is comparable to or higher than the two z ~ 1.5 sBzKs detected in
CO(2-1) previously, suggesting that sBzKs can have a wide range of SFEs.
Comparisons of far-infrared luminosity, gas mass, and stellar mass among the
sBzKs suggest that SDF-26821 is at an earlier stage of forming stars with a
similar SFE and/or more efficiently forming stars than the two z ~ 1.5 sBzKs.
The higher SFEs and specific star formation rates of the sBzKs compared to
local spirals are indicative of the difference in star formation modes between
these systems, suggesting that sBzKs are not just scaled-up versions of local
spirals.Comment: 4 pages, 4 figures, Accepted for publication in PAS
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